The invention relates to an apparatus for braking and positioning a spinning or twisting spindle with the spindle rotor in a specified position, including a spindle brake which is engageable with a rotary part of the spindle and positioning means separate from the brake.
On the basis of their principle of operation, spindle braking and positioning means can be divided substantially into two groups, the first group operating to position the spindle by using external drive means, while the other group employs energy from the spindle drive or the energy produced by braking the spindle for the operation of positioning the spindle.
The present invention relates to an arrangement belonging to the second group, the basic form of which may be substantially as described in German Patent Specifications Nos.: 16 85 934 and 16 85 942. In the arrangement described in German Patent Specification No.: 16 85 942, the spindle rotor, which is driven by a tangential drive belt, is initially brought to a halt by means of the spindle brake while the drive belt continues to act on the spindle rotor. The brake is then released and the rotor, as it slowly starts to move, can again be brought to a halt in an exactly defined preset position by a mechanical locking member which engages in notches or recesses. However, the shocks which occur when the locking member engages may be detrimental to the spindle and its bearings in the long term.
The essential object of braking and positioning means such as are used for example with a pneumatic thread-threading system, is to stop the spindle in a precise predetermined position, it being virtually essential, when mechanical latching or locking members or index pins which engage in recesses are used, that the spindle rotor should, in fact, have been fully braked beforehand so that the latching or locking member can engage in a recess in the spindle rotor or the shaft of the spindle cleanly or freely, and as far as possible without any shock.
Positioning means of this kind which operate essentially by means of inter-engagement are contrasted with braking and positioning means which operate by friction, such as are described, for example, in British Patent Specification No.: 1,357,465. This known arrangement includes a braking shoe for course braking which can be moved up to a braking surface, on a wharve of the spindle, from the outside. Opening at the brake shoe is a passage for compressed air through which compressed air can be fed to build up a cushion of compressed air between the braking surface on the wharve and the brake shoe. This cushion of compressed air forces the brake shoe slightly back from the braking surface on the wharve, with the result that the rotor of the spindle moves slowly round again under the drive torque acting on the spindle until the mouth of a passage arranged in the braking surface on the wharve is opposite the passage for compressed air opening at the brake shoe, when the cushion of compressed air is suddenly released and the brake shoe is re-applied to the braking surface on the wharve. This sudden release of the cushion of compressed air thus results in the spindle rotor being finely braked, or, in other words, exactly positioned, when the two air passages, in the brake shoe and the braking surface on the wharve, are aligned opposite one another.
In contrast to the known braking and positioning means which call for a relatively considerable amount of structural complication and which provide needlessly exact location of the spindle rotor in the preset position, the object of the invention is to enable there to be provided a more simply constructed and thus more reliable spindle braking and positioning means where it is permissible for the spindle to be stopped or locked within a certain angular range about a prescribed central position. It has, in fact, been found that for most purposes where it is necessary for the spindle to be positioned, an example being for the threading of thread through the spindle, it is enough for the spindle or the spindle rotor to be roughly positioned somewhere within a predetermined angular range. This is relevant both to manual and to pneumatic threading.
To achieve this object, there is provided an apparatus for braking and positioning a spinning or twisting spindle with the spindle rotor in a specific position, including a spindle brake engageable with a rotary part of the spindle and positioning means separate from said brake, wherein the positioning means comprises an additional braking surface extending over part of a periphery of a rotary part of the spindle, up to which an additional brake shoe or brake member can be moved. Preferably, the spindle brake is engageable with a wharve of the spindle and the periphery over part of which the additional braking surface extends is a periphery of said wharve. The spindle positioning means involved are means which operate by friction. This is of particular advantage because the spindle, which continues to be subject to the full propulsive torque from the spindle drive after the spindle brake which provides the spindle with its primary braking has been released, is not held and stopped or positioned abruptly but gently.
The additional braking surface, which may be arranged on the outer periphery of a wharve of the spindle in the form of a surface of a thickened portion projecting radially outwards, or on an inner periphery in the form of a surface of an indentation or re-entrant part projecting radially inwards, preferably extends for an angle of from 15.degree. to 30.degree..
The spindle brake proper, i.e. the main device for braking the spindle or for absorbing its energy of rotation, and the positioning means, may have a common actuating mechanism. If, for example, the spindle brake proper, e.g. a brake in the form of an internal or external shoe-brake, and the brake shoe or brake member of positioning means consisting of an additional braking surface and an additional brake shoe or brake member which can be moved up to it, both are engageable in common either with an inner periphery or outer periphery of a wharve of the spindle, preferably they are situated on the wharve braking surfaces at different levels whereby the two brakes do not interfere with each other's operation.
A common actuating mechanism for the spindle brake proper (for coarse braking) and for the additional brake (for fine braking) preferably comprises a toggle lever device which can assume three specified positions and which acts directly on the spindle brake proper and indirectly on the additional brake or brake shoe or brake member through a piston and cylinder means. The three specified positions of the toggle lever device (articulated lever device) in this case can be associated with different braked states, with the added aim of giving an operator the widest possible facilities for control.